Various types of formation and fluid evaluations are performed on oil and gas well before and during production operations. One type of formation evaluation is conducted with downhole nuclear magnetic resonance (NMR) logging. NMR logging, a subcategory of electromagnetic logging, measures the induced magnet moment of hydrogen nuclei (protons) contained within the fluid-filled pore space of a formation. NMR can be used to measure the volume, composition, viscosity, and distribution of these fluids, for example. NMR logging is typically performed by specialized wireline or LWD (logging-while-drilling) NMR logging tools.
NMR logging tools are typically placed close to a wellbore wall to take NMR measurements. The tool body typically includes permanent magnets that generate a static magnetic field and an antenna or radio frequency coil for generating an RF magnet field and detecting the NMR data.